Electronic mail (e-mail) messages are a popular form of communication between parties. Not surprisingly, as e-mail use has increased, e-mail abuse has also increased. For example, e-mail is often used by companies to send unsolicited commercial e-mail (sometimes called SPAM) to masses of people to promote their products or services. E-mail messages are also used to send viruses as attachments that will cause harm if executed, such as by infecting the recipient's computer with some annoying program or by obtaining confidential or sensitive information. More recently, e-mail messages are also being used to send phishing messages that appear to be sent from a source that the recipient trusts and are designed to lure the recipient to a web site that will obtain confidential information from the recipient. It is not uncommon for a particular user to receive dozens or even hundreds of unwanted messages like these every single day. These unwanted messages by their very nature are less secure and potentially more destructive to a user's computer than those that the recipient wanted and/or expected.